After TFS 2008 install with SP1 is complete and you create a team project and try to navigate to the team project site, you may hit an error which says

The permissions granted to user 'domain\user' are insufficient for performing this operation. (rsAccessDenied)

There is a whole lot of help if you google or bing. Here is what I had to do to fix my issue

My setup was three-tier. SQL Server 2008 x64 bit. MOSS 2007 64 bit and TFS 2008 (of course, just 32 bit)

I was accessing the portal site on a windows 2008 box.

I followed this suggestion for the AT (TFS box)

http://msdn.microsoft.com/en-us/library/bb630430/

Basically, I had to repeat the same step but for the team site hosted on the MOSS server. Once I added the MOSS server as the trusted site on IE, the reports started displaying.

Again, this will fix your issue only when all other permissions are set properly on Reporting Services and MOSS. Don't forget that in win2008 you have to start the browser as "Run as administrator" to see TfsReportDS & TfsOlapReportDS links on RS portal. 

Hope it helps!